Recently, with the expected exhaustion of the existing energy resources such as petroleum or coal, there is a growing interest in energy which may substitute for the existing energy resources. As one of these alternative energies, a fuel cell is receiving particular attention due to the advantages in that the fuel cell is highly efficient and does not discharge pollutants such as NOx and Sox, and the fuel used is abundant.
A fuel cell is a power generation system which converts chemical reaction energy of a fuel and an oxidizing agent into electric energy, and representatively, hydrogen and hydrocarbons such as methanol or butane are used as the fuel, and oxygen is used as the oxidizing agent.
Examples of the fuel cell include a polymer electrolyte membrane fuel cell (PEMFC), a direct-methanol fuel cell (DMFC), a phosphoric acid fuel cell (PAFC), an alkaline fuel cell (AFC), a molten carbonate fuel cell (MCFC), a solid oxide fuel cell (SOFC), and the like.
FIG. 1 schematically illustrates the electricity generation principle of a solid oxide fuel cell, and the solid oxide fuel cell is composed of an electrolyte layer (electrolyte) and a fuel electrode (anode) and an air electrode (cathode) formed on both surfaces of the electrolyte layer. Referring to FIG. 1 illustrating the electricity generation principle of the solid oxide fuel cell, oxygen ions are produced while the air is electrochemically reduced in the air electrode, and the produced oxygen ions are transferred to the fuel electrode through the electrolyte layer. Fuel such as oxygen, methanol, and butane is injected into the fuel electrode, and the fuel is bonded to oxygen ions to give out electrons while being electrochemically oxidized, thereby producing water. Electrons move to an external circuit by the reaction.